FIG. 1 illustrates a prior art oil supply system of the type utilized in integrated drive generators manufactured by the assignee of the present invention for use in the Boeing 757 and 767 aircraft. The integrated drive generator has an oil supply system 10 which controls the level of oil in the overall case 12 of the integrated drive generator by pumping oil from the case into a tank 14. It should be understood that the sump 16 has been illustrated symbolically when in fact it is in the bottom of the case 12. The purpose of the tank 14 is to hold a portion of the overall volume of oil in the case 12 while maintaining the oil level in the sump 16 below a level which would interfere with the overall operational efficiency of the rotating mechanical components of the integrated drive generator and further prevent the possibility of thermal runaway caused by substantial contact with mechanical components rotating at high rotational velocities. The tank 14 has a drain 18 in the top to permit oil to flow from the tank into the sump 16 under inverted flight or rapid descent conditions.
The oil contained in the tank 14 is controlled as follows. A scavenge pump 22 and an inversion pump 24 respectively pump oil from the sump 16 in non-inverted and inverted orientations or rapid descent conditions to a deaerator 26 through an oil circuit containing filter 28 and heat exchanger 30. Oil normally flows through the filter 28 to the heat exchanger 30, which is external to the case 12, to the inlet of deaerator 26 which supplies pressurized oil at a first output to the inlet of charge pump 32 and a mixture of oil and air at a second outlet to the sump 16. Relief valve 34 functions to open when the pressure on the output of the scavenge pump 22 exceeds a predetermined pressure. The relief valve 34 shunts oil back to the inlet of the scavenge pump 22 when the pressure at the outlet of the scavenge pump 22 exceeds the pressure limit of the relief valve to regulate the output pressure of the scavenge pump. Indicator 38 provides a visual indication to service personnel that the filter 28 is in need of service. Relief valve 40 provides a bypass of the heat exchanger 30 when the pressure drop across the heat exchanger exceeds a predetermined limit to insure a proper volume of oil flow to the inlet of the deaerator 26. During inverted operation or rapid descent conditions, oil may flow from the top 18 of tank 14 to the sump 16 to make up any deficiency of oil in the sump pumped to the charge pump 32 by the inversion pump 24. The tank 14 is fed oil from the charge pump 32 through inlet 33 during operation of the integrated drive generator 10. Drain 35 permits oil to flow from the tank 14 to sump 16 when the integrated drive generator is not operating so that the oil level in the sump rises to a level to facilitate the checking of the level by service personnel. The oil output of the charge pump 32 is connected in parallel to the rotor 48 of the three phase alternating current generator 46 to lubricate the bearings, cool the interior of the rotor by axial flow through the rotor and cool the diodes and end turns of the stator 44 which oil flows to the sump 16, to the differential 50 of a constant speed drive transmission 52 which oil flows to the sump, and to a pair of hydraulic pump and hydraulic motor combinations 56 of the constant speed drive transmission. The output oil from the pair of hydraulic pump and motor combinations is fed back to the input of charge pump 32 through charge relief valve 60 which regulates the output pressure of the charge pump.
A power takeoff 54 from the airframe propulsion engine is coupled to the hydraulic pump and motor combinations 56 and to the differential 50 in a manner conventional in an integrated drive generator. The output 57 of the hydraulic pump and motor combinations 56 is coupled to the differential 50 in the conventional manner. The constant velocity output 59 of the differential 50 is coupled to the rotor 48 of the alternating current generator 46 in the conventional manner. Governor 65 and control piston 67 are conventional controls of the hydraulic pumps.
U.S. Pat. No. 4,600,413, which is assigned to the assignee of the present invention, discloses a centrifugal deaerator and pump. The 3413 teaches that the output of the deaerator is coupled to an oil reservoir such as a housing for collecting oil. When the oil reservoir is in an inverted position, oil from the oil reservoir may flow back into the opening of the deaerator for outputting an oil air mixture through the deaerator to the deaerated oil output to the charge pump 32.
The prior art system of FIG. 1 suffers from the deficiency that it does not supply make up oil from the tank 14 to the charge pump 32 when the output from the deaerator 26 is insufficient during normal operation. With the prior art, orientations inclined from the horizontal, such as 45.degree., present potentially serious problems to the supply of pressurized oil to the components of the integrated drive generator requiring lubrication. When the aircraft is inclined from the horizontal, the level of oil in the sump 16, which is supplying oil to the scavenge pump 22, can be substantially changed which can prevent the scavenge pump 22 from pumping sufficient oil to the deaerator 26. At this angular orientation, the inversion pump 24 is likely to be totally ineffective in pumping oil for the reason that there is no pool of oil in proximity to the intake of the inversion pump. In an orientation inclined from the horizontal such as 45.degree., the coupling of the top of tank 14 through drain 18 to the sump 16 is not effective in providing oil to the intake of the scavenge pump 22 to make up for any deficiency of the oil being pumped by the scavenge pump. Because of the high rotational speeds of components in the integrated drive generator, any serious deficiency in the output of the oil pump by the charge pump 32 can lead to increased wear, loss of speed control by the hydraulic pumps and motors, or premature failure. Accordingly, the prior art of FIG. 1 does not insure that sufficient oil will be provided by the charge pump 32 to the critical components requiring pressurized oil during the operation of the integrated drive generator.
The assignee of the present application has manufactured integrated drive generators which include a dual port relief valve which functions to shunt oil from the output of the scavenge pump or inversion pump to the sump when the output pressure exceeds a pressure limit of the relief valve when the temperature of the oil is above a predetermined temperature and which functions to shunt the oil back to the input of the scavenge pump when the pressure limit is exceeded and the temperature of the oil is below the predetermined pressure for the purpose of rapidly warming the oil.
The assignee of the present invention has manufactured integrated drive generators which use oil to cool the stator of the main alternating current generator. An oil cooling circuit is contained in the back iron of the stator which receives pressurized oil from the charge pump and discharges oil into the oil sump.
The assignee of the present invention has manufactured integrated drive generators having an aspirator for removing water from oil within the integrated drive generator. The aspirator uses pressurized oil from the charge pump to draw in air from outside the case of the integrated drive generator through a duckbill valve. Oil utilized by the aspirator is discharged into the oil sump.